Area Calculator
Pick a shape, enter its dimensions, read the area — six common 2-D shapes with exact formulas and live updates.
How to use
- Choose the shape from the dropdown.
- Fill in the base, height or radius fields that appear.
- The area updates instantly as you type.
Frequently asked questions
Which shapes are supported?
Six: square (s²), rectangle (w × h), circle (πr²), triangle (½ × base × height), trapezoid (½ × (a + b) × height) and parallelogram (base × height).
Why does the circle formula involve π?
A circle’s area equals π times the radius squared — one of geometry’s defining results. The π constant means circle areas are irrational unless the radius itself contains π, so results are shown with 6 significant digits.
Which height does the triangle formula need?
The perpendicular height from the base to the opposite vertex — not the length of a slanted side. If you only know three sides, use the triangle’s perimeter tool here, or compute the height via Heron’s formula elsewhere.
What counts as a trapezoid’s two bases?
The two parallel sides, labelled a and b. The height is the perpendicular distance between them. Unlike a parallelogram, the bases differ in length — that is exactly what the ½(a + b) averages.
Can I compute in any unit?
Yes — the formulas are unit-agnostic. Enter all lengths in the same unit and the area comes out in that unit squared (cm in → cm² out). Mixing units in one shape is the classic mistake this tool can’t fix for you.